<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>moon</title>
    <style>
      .center {
        position: absolute;
        margin: auto;
        top: 0;
        right: 0;
        bottom: 0;
        left: 0;
        width: 100px;
        height: 100px;
        background-color: transparent;
        border-radius: 50%;
        box-shadow: 25px 10px 0px 0px grey;
      }
    </style>
</head>

<body>
    <div class="center"></div>
</body>
</html>
